This is a calculation of the amount of ballast that must be removed from the F1 load in order to bring it to nominal height.

Current conditions:

• In vacuum.
• Temperature: 23 degrees (klog 15070).
• F1 keystone position with control off: h=-429 µm (klog 15070). 

Other parameters:

• Measured resonance frequency: 340 mHz (kog 5334).
• Load on F1: 157.53 kg (JGW-T2012030, likely SR2 values, see notes in document page).
• k = 718.92 N/m.

Using this information, it's easy to calculate that to lift the keystone by 429 µm, it's necessary to remove 31 grams.

I also checked the data measured when F1 filter was tuned in order to check the resonant frequency expected at h=-429 µm.

• Data in klog 15101.
• I fitted a parabola to the data of frequency versus height.
• During installaton zero displacement corresponds to a height 65.5 mm per the 3D CAD in all F1 and BF units.
• For h = 0 µm, f = 315 mHz (less than the measured value of 340 mHz per kog 5334).
• For h = -429 µm, f = 322 mHz.

The discrepancy likely comes from the fact that the frequencies are usually measured by visual inspection and not necessarily so precise. According to this data and calculation, less than 31 grams would be needed.

This calculation will be review once I calculate how much we need to remove from the IM to bring the BF keystone to nominal position.